1. Field of the Invention
The present invention relates to telecommunications systems, and in particular, to an improved system and method for detecting loop start and ground start trunks.
2. Description of the Related Art
Loop start and ground start are the most common methods of signaling when a subscriber places a call to a central office through a private branch exchange. In loop start signaling to initiate a call, the PBX goes off hook closing the tip ring two wire loop. The central office detects the current flow and returns a dial tone. In ground start signaling to initiate a call, the PBX grounds the ring lead, which is sensed by the central office. The central office then grounds the tip lead. The PBX senses the tip ground and closes the two wire loop, and then removes the ring ground.
A feature provided in some systems is xe2x80x9cfar end disconnection.xe2x80x9d In a loop start system, this means that the central office interrupts the loop to signal the PBX a disconnection of the call attempt or completed call (i.e., a call to a non-existent number or to signal the CO customer went on hook after a conversation). Correspondingly, in a ground start system, the central office will disconnect tip from ground. As can be appreciated, the PBX must have its trunk interfaces properly configured for far end disconnection. If the trunk interfaces are configured improperly, the trunks will be unusable. Often, PBX trunk interfaces are provided with circuitry to implement both loop start and ground start signaling. If the configuration information provided by the documentation is incorrect or unavailable, than improper configuration may be installed.
As such, there is a need for a system to identify whether far end disconnection indication is provided.
These and other drawbacks in the prior art are overcome in large part by a system and method for automatic configuration of telephone trunks according to the present invention.
Telephone equipment, such as a private branch exchange (PBX) is provided according to an implementation of the present invention. The telephone equipment includes one or more trunk interface cards. The trunk interface cards are configurable by software to operate with ground-start or loop-start trunks. According to the present invention, the trunk interface cards are controllable by software to determine which type of trunk they are connected to and to determine if the connected central office provides for far-end disconnection indication.
According to an implementation of the present invention, a trunk interface closes the tip-ring loop, checks for dial tone, and dials a predetermined, disconnected or dummy test telephone number. If the central office disconnects the dial tone after the first dialed digit, the trunk is determined to be a loop-start trunk. The trunk interface waits for the time-out period to elapse and checks if the central office disconnects the loop. If so, the central office provides far-end disconnection indication for the loop trunk.
If the system determines the interface is not a loop start trunk, the system then determines if the connection is ground-start. The Ring lead is connected to ground and the interface monitors whether the tip lead goes to ground. If so, the two-wire loop is closed and the system checks for dial tone, dials a predetermined test number and checks if dial tone is disconnected by the central office after the first digit was dialed. If so, the connection has the correct polarity. The interface then waits the time out period from the central office indicating incomplete dial and determines whether the central office disconnects the tip lead from ground. If so, the central office provides far-end disconnection indication for the ground start trunk. If the connection was determined to not have the correct polarity, an error indication is generated indicating that the tip and ring wires are to be reversed.